Navigation systems of the generic type are used, for example, as mobile navigation devices in order to guide the driver of a motor vehicle from a starting point to a destination. In this case, the navigation device scans the data of a database, in which a geographic area is described in the form of road segments and junctions. Consequently, the database contains a network of road segments and intermediate junctions that describe the road system, particularly the road network, in a certain form and therefore allow the processing in a data processing system by means of corresponding computing algorithms. A route in the form of a sequence of road segments and junctions that guides the user from the starting point to the destination is selected from the data of the database by means of a suitable routing computation method.
However, known navigation systems not only compute the route from the starting point to the destination. These navigation systems also compute maneuvering information that contains instructions for the user in order to carry out maneuvers that follow the route from the current position along the route. For example, if the user reaches a road intersection, maneuvering instructions are computed that inform the user of the direction, in which he needs to turn at the road intersection.
The output of the maneuvering instructions for the user can be realized in different ways. The maneuvering instructions are usually output acoustically in the form of a voice announcement. During a turning maneuver at an intersection, for example, the following announcement may be output: “Please turn left at the next intersection”. However, maneuvering instructions that are output acoustically have the disadvantage of no longer being continuously available to the user after the announcement. If the user did not understand the acoustic maneuvering instructions, it is either necessary to repeat the maneuvering instructions or the user needs to continue maneuvering without corresponding instructions. In order to solve this problem, known navigation systems also feature so-called schematic maneuvering images. In the schematic maneuvering image, at least the next maneuver to be executed and/or the maneuver to be executed after the next maneuver is graphically illustrated in schematic form and this graphic illustration is continuously displayed on a display device until the corresponding maneuver is executed. For example, if the user reaches an intersection between two roads, the schematic maneuvering image may consist of a schematic road intersection in the form of an orthogonal cross and the turning direction required in accordance with the maneuvering instructions is displayed in the form of a motion arrow.
The computation and display of the schematic maneuvering image represents an additional computation process during the operation of a navigation system that is particularly time-critical in the real-time mode of mobile navigation devices. During the computation of the schematic maneuvering image that is known from the state of the art, one therefore only resorts to data that is already known from the route computation. In other words, this means that the known methods for computing and displaying a schematic maneuvering image only take into account junctions and road segments that lie along the route itself. In addition, road segments that intersect or converge with the computed route, i.e., road segments that share at least one junction with the route, may also be incorporated into the schematic maneuvering image. This method of computing the schematic maneuvering image is based on the notion that it suffices to display the roads and junctions along the route to the user in the schematic maneuvering image in order to enable the user to execute the maneuver.
In practical applications, however, this notion has proved to be incorrect in certain instances. Particularly at confusing road configurations, for example, at intersections with a number of intersecting roads, it does not suffice for the optimal orientation of the user to merely display the roads and junctions that lie along the route to the user in the schematic maneuvering image. On the contrary, such a schematic maneuvering image that only illustrates part of the actual road situation can contribute to the confusion of the user, for example, because it is not possible to recognize on which of the different roads the user should turn at a confusing intersection. Consequently, maneuvering instructions that are output acoustically or optically have the disadvantage of frequently being ambiguous.